A variety of monoclonal antibodies have been recently developed that distinguish among classes of normal human lymphocytes and identify discrete stages of differentiation. We are using a abattery of these antibodies to determine the phenotypes of human malignant lymphomas using a Fluorescence Activated Cell Sorter (FACS-II). The phenotypic expression of these neoplastic lymphocytes is then related to normal lymphocytes and is useful in diagnosis and monitoring of patients' tumors during therapy. The diagnosis of B-cell neoplasms is aided by demonstrating monoclonality with anti-immunoglobulin light chain staining, cytoplasmic RNA blots and genomic DNA (Southern) blots.